You asked what you can do to improve you photos. Getting a tripod will help in low light situations like the waterfall, but the biggest thing you should work on is composition and technique. For example, the waterfall shot. You did good by putting the top of the waterfall in the upper third of the frame, but otherwise it's a static shot that just sits there. What if you shot the waterfall from the side, with your camera much closer? That would put the water closer to the viewer perhaps creating a more dynamic frame.

Since you said it was near dusk, if you used a tripod (I know you don't have one yet) to steady your camera and shoot with a 1 sec. exposure, you will blur the moving water but leave the rocks and surrounding area sharp (assuming that you didn't move the camera during the exposure). You did this to a small degree in your photo, but a slightly longer exposure time will enhance the effect.

Photos of static objects must have good composition and/or lighting if they are to stand out.

Keep working at it and pretty soon you'll find that you're shooting great shots.